A multi-layer wiring substrate is known as a substrate to have semiconductor elements, such as a semiconductor IC circuits or the like, thereon. The multi-layer wiring substrate includes insulating layers and wiring conductors, which are stacked one over another.
A build-up method is known as a method of manufacturing such multi-layer wiring substrate. The resulting multi-layer wiring substrate has a lower insulating layer, a lower conductor layer (wiring conductor) formed on the lower insulating layer, an upper insulating layer formed on the lower insulating layer and the lower conductor layer, and an upper conductor layer (wiring conductor) formed on the upper insulating layer. Via holes are formed in the upper insulating layer such that the via holes extend downward to the lower wiring conductor. Part of the upper wiring conductor is applied on the interior of each via hole to connect the upper wiring conductor to the lower wiring conductor. Such technique is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2010-205801 (Patent Literature Document 1).
FIGS. 6(A) to 6(C) of the accompanying drawings show part of a method of manufacturing a multi-layer wiring substrate, which is disclosed in Patent Literature Document 1.
(A) An upper insulating layer 33 is formed on top of a lower insulating layer 31. A wiring conductor 32 is also formed on the lower insulating layer 31.
(B) Part of the upper insulating layer 33 is removed by, for example, a laser beam or a drill to create a via hole 34. In this process, smear S that is derived from the material of the upper insulating layer 33 inevitably remains.
(C) In order to remove the smear S, a desmear process (smear removing process) is applied such that the smear is dissolved with, for example, an alkaline solution. Then, an upper surface of the wiring conductor 32 is exposed.
In this manner, the dissolving process with the alkaline solution is needed to remove the smear S on the upper insulation layer 33. This process is in fact irrelevant to the method of manufacturing the substrate itself, and entails a wet process to be applied to the entire substrate. Thus, there is a problem, i.e., a throughput is not good.
To avoid such problems, the conventional wet method that relies upon the alkaline solution is not used in the desmear treatment during the substrate manufacturing process. Instead, a dry method (dry process) is recently studied, i.e., a method of removing the smear with an ashing treatment is studied.
There is another problem. Specifically, a high cost is needed to treat a high-density alkaline waste solution that results after the method using the alkaline solution is performed, and a high cost is needed to treat a low-density alkaline waste solution that results after a subsequent rinsing process or the like.
One of the recently studied dry methods that use the ashing process includes placing a substrate (object to be treated) in an atmosphere containing oxygen, and irradiating the object with an ultraviolet beam at a wavelength of 200 nm or shorter (vacuum ultraviolet beam) to decompose and remove an organic substance. If the desmear treatment is carried out by the dry method in the above-described manner, the rinsing process and the drying process become unnecessary. Note that the rising process and the drying process are necessary after the desmear treatment, if the desmear treatment is carried out by the wet method. Also, if the desmear treatment is carried out by the dry method, there is no waste solution, and it is possible to smoothly proceed to a next process. This can significantly reduce the manufacturing cost.
Such ashing apparatus is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 2007-227496 (Patent Literature Document 2) and Japanese Patent Application Laid-Open Publication No. 2011-181535 (Patent Literature Document 3). These patent literature documents teach an ashing apparatus that includes a lamp for emitting an ultraviolet beam, and irradiates a work with a beam (vacuum ultraviolet light) through a quartz glass window.
The ashing apparatus disclosed in Patent Literature Document 2 includes a protecting tube and an ultraviolet lamp received in the protecting tube. A work is placed in a chamber, and the ashing treatment is applied to the entire sheet of work. The ashing apparatus of this Patent Literature Document performs the ventilation while introducing an inert gas into the chamber during the ashing treatment, or only performs the ventilation of the chamber during the ashing treatment.